1. Field of the Invention
The present invention relates to a video presenter, more particularly, to an illumination device for illuminating a target object placed on a video presenter.
2. Description of the Related Art
Video presenters are devices that input and display an image of a target object taken typically by a charge coupled device (CCD) camera on a display unit for academic or commercial purposes. Particularly, a video presenter can obtain an enlarged image of the target object taken from the CCD camera by coupling a magnifying lens to the CCD camera and can display the enlarged image of the target object on the display unit. The video presenter may include an illumination device for improving the definition of an image of the target object taken by the CCD camera. The illumination device should appropriately illuminate the target object while preventing itself from interfering with a camera head of the CCD camera. The illumination device is typically designed to have a compact size and a simple structure for easy manipulation or to save the manufacturing cost.
FIG. 1 is a perspective view of a typical video presenter. Referring to FIG. 1, a video presenter includes first and second camera support arms 12 and 13 connected together and disposed at one side of a table 11, a camera head 15 supported by the first and second camera support arms 12 and 13, first and second lamp supporters 16 and 17 disposed at opposite lateral sides of the table 11, and first and second lamps 18 and 19 supported by the first and second lamp support arms 16 and 17, respectively. The first and second camera support arms 12 and 13 are mounted to table 11 of the video presenter so that the second camera support arm 13 can rotate with respect to the first camera support arm 12 about a rotation axis or pivot shaft 14. The lower end of the first camera support arm 12 is rotatably fixed to the table 11. The first and second lamp supporters 16 and 17 are fixed to the table 11 so that their lower ends can be rotated and tilted laterally. The camera head 15 is rotatably supported by the second camera support arm 13 at the upper end thereof. The first and second lamps 18 and 19 are rotatably fixed to the first and second lamp supporters 16 and 17 at the upper ends thereof, respectively.
FIG. 2 is a front view of the video presenter of FIG. 1 with the lamp directed in an illumination position. Referring to FIG. 2, the first and second lamp supporters 16 and 17 can be adjusted to tilt about a horizontal plane so that they can form a predetermined angle a with the horizontal plane. Accordingly, light emitted from the first and second lamps 18 and 19 can be appropriately distributed on the top surface of the table 11 by lifting, lowering, or tilting the first and second lamp supporters 16 and 17.
The video presenter of FIGS. 1 and 2 can provide an optimum illumination to the target object by allowing a user to freely lift or lower or adjust the first and second lamp supporters 16 and 17. However, when adjusting the first and second lamp supporters 16 and 17, rotation joints on the first and second lamp supporters 16 and 17 rub against the first and second lamp supporters 16 and 17. Therefore, after a long period of use, the rotation joints may substantially be worn out or loosened.
Japanese Patent Application Publication No. 8-186743discloses a video presenter, in which an illumination device is provided at only one side of a target object. With this illumination device, however, light cannot be evenly distributed throughout the target object area. Moreover, as the intensity of illumination is inversely proportional to a square of the distance between the target object and the illumination device, the closer a portion of the target object is to the illumination device, the more the portion of the target object is illuminated. Likewise, the farther a portion of the target object is from the illumination device, the less the portion of the target object is illuminated. In addition, the intensity of illumination varies depending on an incidence angle of light emitted from the illumination device. Therefore, in such a device where the illumination device is provided at only one lower side of the target object, it is difficult to apply light to the target object with an adequate incidence angle.
In addition, the video presenter disclosed in Japanese Patent Application Publication No. 8-186743 illuminates the target object with a reflection plate which reflects light emitting from a light source. The reflection plate should be positioned above the target object in order to properly illuminate the target object. However, because the reflection plate is fixed on the table of the video presenter, it is not intended to adjust its orientation for a better illumination. Thus, if the operator attempts to adjust the reflection plate, she can be injured by the reflection plate or the reflection plate may be damaged or deformed beyond its design limit.
Japanese Patent Application Publication Nos. 9-205527 and 9-205566 each disclose a video presenter, in which a light source is mounted in the vicinity of the lens in a camera head. Since the light source is a distance apart from a target object, the target object may suffer from lack of sufficient illumination. Thus, there is a strong need to increase the illumination intensity of the light source. In order to increase the illumination intensity of the light source, however, a considerable amount of energy should be consumed, which may often cause noises in circuits near an optical photographing system. In addition, there is also a possibility of image deformations especially when the surface of the target object is reflective.
Japanese Patent Application Publication No. 2000-138796 discloses a video presenter using a light emitting diode (LED) as light source. Given that an LED only emits a small amount of light, many LEDs are necessary to provide a sufficient amount of light to the target object. In addition, a convex lens should be coupled to each of the LEDs. Moreover, a prism element should also be coupled to each of the LEDs in order to disperse or collect light radiated from the LEDs. Therefore, the structure of the video presenter inevitably becomes complicated, which results in an increase in the manufacturing costs of the video presenter.
For a video presenter, in order to illuminate a target object with sufficient light, it is more important to evenly and adequately distribute light radiated from an illumination device over the entire surface of the target object rather than focusing a considerable amount of light on only a central portion of the target object.